Abstract
By means of two-photon excited photoluminescence, we demonstrate the influence of self-absorption on the emission properties of thin (1.5 microm) film CdS formed by laser ablation. The excitation of the sample is performed with 200 fs pulses at 804 nm (1.54 eV). The photoluminescence spectrum takes the form of a single peak centered at 510 nm (2.43 eV) at 300 K. The spectrum is shifted about 45 meV to lower energies with respect to the photoluminescence excited by one photon absorption. By fitting the photoluminescence spectra with the Roosbroeck-Shockley relation and Urbach's rule, it is shown by Beer's law that the shift is caused by self-absorption. The results further provide evidence of low impurity concentration and excellent surface quality. They also confirm the outstanding optical properties of thin film CdS formed by pulsed-laser deposition and suggest the application of the films for effective up-conversation materials in ultra-fast experiments.
Highlights
The II-VI compound semiconductor CdS has various appealing features for technical applications, such as the “green bandgap” at around 2.45 eV, dichroism and a spectral dependence of the photocurrent action spectrum, which is very similar of that of the human eye
By means of two-photon excited photoluminescence, we demonstrate the influence of self-absorption on the emission properties of thin (1.5 μm) film CdS formed by laser ablation
The excitation of the sample is performed with 200 fs pulses at 804 nm (1.54 eV)
Summary
The II-VI compound semiconductor CdS has various appealing features for technical applications, such as the “green bandgap” at around 2.45 eV, dichroism and a spectral dependence of the photocurrent action spectrum, which is very similar of that of the human eye. At 300 K, either no photoluminescence was observed or the spectra are clearly shifted to the red spectral range with respect to the bandgap. It was shown that by pulsedlaser deposition the emission features of CdS films are appreciable improved. We demonstrate the influence of self-absorption on the photoluminescence of thin film CdS by two-photon photoluminescence. Two-photon photoluminescence in CdS is investigated since the early 1960’s [10] and regained considerable interest recently because of the appearance of femtosecond lasers, whose excitation causes pure carrier effects without absorption variations due to undesired thermal effects [11]
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